At the arena, Calvin Klein was spotted passing through the Barclays’ “Calvin Klein VIP entrance” on Atlantic Avenue, along with Sting, Michael Strahan and Barbara Walters.

Behind the scenes, Donna Karan was dressing Streisand backstage.

“My mom knows Barbra’s body so well she can design for her in her sleep,” Karan’s daughter, Gabby, was overheard saying in a VIP section.

Streisand’s ex-husband, Elliott Gould, meanwhile, was seen in the audience in tears when son Jason Gould, 45, dueted with his mom onstage.

“The most emotional part of the three-hour show was Jason singing with his mother,” said an insider. “It wasn’t till Barbra’s recent 70th birthday — when Jason made a ‘Happy Birthday’ video and sang, sounding very much like his mother — that Barbra knew he had her pipes. Jason never performed before.”

At a 40/40 Club after-party, Streisand was “mobbed by friends,” including Ralph Lauren, Michael Kors, Rosie O’Donnell, Regis Phibin and Gerard Butler, “who starred in ‘Phantom of the Opera’ and is a big Barbra fan,” a source said. Perhaps those who chowed down at Peter Luger were lucky, as the spread at the party was “fruit, marshmallows, brownies, cookies and coffee.”

Said a VIP, of the crowd, “It was like the rich previously from Brooklyn,” including Woody Allen.